Electroluminescent panels are used in a variety of lighting applications where low power consumption, extended lifetime and compact size are desired. Examples of such applications include illuminated exit signs, outdoor address plaques, and the like. The electroluminescent panel is generally connected directly to an AC source, and provides a light output which is a function of the applied voltage and frequency. Power consumption is very low, typically on the order of 0.1 watt.
The principal drawback of electroluminescent panels is low light output. A typical electroluminescent panel construction consists of a steel substrate carrying various dielectric, phosphor and conductive layers that are applied by screen printing or spraying. By optimizing the fabrication process, the light output of the resulting electroluminescent panel can be increased considerably. However, there is a practical limit on the light output that can be obtained without increasing the operating voltage or frequency of the panel.
An increase in the operating frequency of an electroluminescent panel, while possible in theory, requires a substantial investment in additional circuitry. This is undesirable for many of the applications in which electroluminescent panels are used, since the cost of the resulting product is increased and its reliability may be adversely affected. The other method of increasing brightness is to increase the operating voltage of the panel, which can be done by means of a transformer. However, the additional cost and weight of a transformer is undesirable in many applications, and the losses introduced by the transformer can reduce the operating efficiency of the electroluminescent panel. Accordingly, a need exists for a simple method of increasing the light output of an electroluminescent panel, without significantly affecting its cost, operating efficiency or reliability.